Steering wheel position sensors are used in automotive applications for electronic monitoring of steering functions of a motor vehicle. An example of a current steering wheel position sensor is depicted at FIGS. 1 through 5.
The prior art steering wheel position sensor 10 uses non-contacting Hall effect sensor technology, producing dual outputs of indication of steering wheel rotation: a coarse output and a fine output. The conventional steering wheel sensor 10 is designed for electronic control systems requiring steering wheel position input. Typical applications of the conventional steering wheel position sensor 10 include, for example, chassis controlled stability enhancement systems, electrically assisted power steering, steer-by-wire systems and navigation systems.
As shown at FIGS. 1 and 2, the conventional steering wheel position sensor 10 includes a housing 14 having a mounting hole 16. The conventional steering wheel position sensor 10 is mounted to the steering column 12 (shown at FIG. 1) via the steering column passing through an engagement aperture 20 of a large main gear 22, wherein the hole 16 and the engagement aperture 20 are concentrically aligned with each other. When the steering wheel of the motor vehicle is turned, the steering column 12 rotates the main gear 22 inside the housing 14. The main gear 22 has teeth 22a which rotatably drive a small auxiliary gear 24 via its respective teeth 24a enmeshed therewith. Both of the main and auxiliary gears 22, 24 are composed of DELRIN 100 (DELRIN is a registered trademark of DuPont for an acetal resin material), and each respectively therewithin contain an annular permanent magnet 26a, 26b(see FIG. 5). Two linear Hall effect sensors 28a, 28b sense magnetic field rotation of the main gear 22. A pair of linear Hall sensors 28c, 28d; arranged perpendicularly relative to each other (shown best at FIG. 4), sense the magnetic field rotation of the auxiliary gear 24. Signals from all four sensors 28a, 28b, 28c, 28d are acquired by a microcontroller 30 and processed to find the instantaneous angle of rotation of the steering column 12. This angle is then used to set the values of the duty cycle for both pulse width-modulated outputs. The microcontroller 30 simultaneously produces two pulse width-modulated outputs based on the values previously set: one output with coarse resolution and a second output with fine resolution, which appear, via suitable wiring, at wires emanating from an electrical connector 18.
As can be understood by reference to FIGS. 3 through 5, the auxiliary gear 24 has an annular lip 24b and an annular base 24c connected to the annular lip (see FIG. 5). The auxiliary gear 24 is rotatably interfaced with a ring shield 32 in the form of an annular ring shield wall 32a which confines the magnetic field of the auxiliary gear. The ring shield 32 provides a gear bearing 34 for the auxiliary gear 24 at two locations of guidance for the auxiliary gear, an upper guide surface 34u at the top surface of the ring shield wall which slidingly abuts the annular lip 24b and an inner guide surface 34i of the inside surface of the ring shield wall which slidingly abuts the annular base 24c. Both of the guide surfaces 34u, 34i involve sliding friction at the aforesaid abutments with the auxiliary gear 24. Further, the annular magnet 26b of the auxiliary gear 24 tends to attract the ring shield 32, causing frictional effects (ie., wear, heat, vibration, noise, back lash, etc.) between the auxiliary gear and the upper and inner guide surfaces 34u, 34i to be enhanced.
While the conventional steering wheel position sensor 10 performs quite admirably, it would be desirable, if somehow possible, to eliminate the frictional effects which occur between the auxiliary gear and the ring shield.